Polymer electrolyte battery

ABSTRACT

In a polymer electrolyte battery including a battery element having a cathode and an anode coiled through a polymer electrolyte, a section of the battery element perpendicular to the coiling axis has a curved form. As compared with a polymer electrolyte battery having a flat plate type battery element curved, the former battery has an extremely low possibility of short-circuit at the end of an electrode and excellent battery characteristics.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. application Ser. No. 10/181,504 filed onOct. 7, 2002, now U.S. Pat. No. 7,163,762, which is a national phase ofPCT/JP01/10183 filed Nov. 21, 2001, which claims priority to Japaneseapplication 2000-354871 filed Nov. 20, 2000, which are incorporatedherein by reference to the extent permitted by law.

FIELD OF THE INVENTION

The present invention relates to a polymer electrolyte battery having abattery element in which a cathode and an anode are coiled through apolymer electrolyte and a method for manufacturing it, and moreparticularly to an improvement of the form of the battery element.

BACKGROUND

In recent years, as portable electronic devices are made compact and theweight of them are reduced, it has been highly demanded for batterieswhich supply electric power to these electronic devices to decreasetheir size, thickness or weight irrespective of uses thereof such asdriving means or backup means.

As a battery for satisfying such a demand, has been developed and putinto practical use a nonaqueous electrolyte battery, what is called alithium battery which includes a cathode and an anode having activematerials capable of reversibly inserting and extracting lithium ionsand a nonaqueous electrolyte and has such advantages as a high outputand high energy density.

Especially, the lithium battery including a polymer electrolyte as thenonaqueous electrolyte has characteristics that the battery is excellentin its leak resistance and high in its safety. Further, since thelithium battery including the polymer electrolyte is light in its weightand may be thinned in this thickness, the configuration of the batterycan be designed so as to meet the forms or size of various kinds ofelectronic devices. Therefore, this lithium battery has a feature thathas not been seen in the conventional batteries.

For example, when a thin and flat plate type polymer electrolyte batteryis produced, a battery element may be formed by providing a polymerelectrolyte between a thin sheet type cathode and a thin sheet typeanode and the battery element may be covered with a laminate film havingan aluminum foil as a core material.

Nowadays, in order to make various types of electronic devices morecompact, it has been necessary to efficiently employ the inner spaces ofthe electronic devices, and it has been especially demanded to use theinner spaces having curved surfaces as spaces for accommodating thebatteries serving as the power sources of the electronic device.

However, for instance, as shown in FIG. 1, when a flat plate typepolymer electrolyte battery 102 is attached to an inner space having acurved surface in a portable electronic device 101 such as a portabletelephone or a PDA, useless spaces 103 are inconveniently generatedbetween the casing of the electronic device 101 and the flat plate typepolymer electrolyte battery 102 so that the inner space of theelectronic device 101 cannot be efficiently used.

Thus, as a method for efficiently using these spaces 103, the flat platetype polymer electrolyte battery 102 may be curved so as to meet theform of the inner space of the electronic device 101.

However, since the flat plate type polymer electrolyte battery 102 has aflat plate type battery element including a thin sheet type cathode anda thin sheet type anode and a polymer electrolyte interposedtherebetween, even when the flat plate type polymer electrolyte battery102 is curved, a desired curved form cannot be held for a long time.Further, an electrode active material layer may be cracked or furthermay be separated from a current collector due to an external force whenthe flat plate type battery element is bent. Therefore, when the flatplate type polymer electrolyte battery 102 is bent, batterycharacteristics are disadvantageously extremely deteriorated.

For example, in Japanese Patent Application Laid-Open No. hei 11-307130,is disclosed a method for bending a flat plate type battery element byapplying a thermocompression bonding process to the battery element(refer it to simply as a flat plate type battery element, hereinafter)having a cathode and an anode laminated through a polymer electrolyteusing two rolls respectively having different diameter. According tothis method, although the curved configuration of the battery element ismaintained, a shearing stress by the rolls with different diameter isexerted on a part between an active material layer and a currentcollector, so that the resistance of a cell is undesirably increased, ashort-circuit is apt to be generated at the end of a stacked electrode,and accordingly, a stable battery performance cannot be inconvenientlyobtained. Further, not only the curvature of a desired curvedconfiguration can be extremely hardly obtained, but also the thicknessof a cell is inconveniently greatly regulated.

SUMMARY

The present invention is proposed by taking these conventionalcircumstances into consideration and it is an object of the presentinvention to provide a polymer electrolyte battery in which apossibility of short-circuit is low in the end part of an electrode andbattery characteristics are good even when the electrode has, forinstance, a curved form or a semicircular curved surface so as to beadapted to the form of each of the inner spaces of various kinds ofelectronic devices and a method for manufacturing it.

For achieving the above-described object, a polymer electrolyte batteryaccording to the present invention includes a battery element having acathode and an anode coiled through a polymer electrolyte, wherein asection of the battery element perpendicular to the coiling axis has acurved form.

The polymer electrolyte battery according to the present inventionconstructed as mentioned above includes a battery element having acathode and an anode coiled through a polymer electrolyte whose sectionperpendicular to the coiling axis of the battery element has a curvedform. Therefore, when the polymer electrolyte battery of the presentinvention is compared with a polymer electrolyte battery having a flatplate type battery element curved, the former battery has an extremelylow possibility of short-circuit at the end of an electrode andexcellent battery characteristics. Further, in the polymer electrolytebattery according to the present invention, at least a part of thecurved form may have a flat part.

Further, a polymer electrolyte battery includes a battery element havinga cathode and an anode coiled through a polymer electrolyte, wherein asection of the battery element perpendicular to the coiling axis has asemicircular form.

The polymer electrolyte battery according to the present inventionconfigured as mentioned above includes a battery element having acathode and an anode coiled through a polymer electrolyte whose sectionperpendicular to the coiling axis of the battery element has asemicircular form. Therefore, when the polymer electrolyte battery ofthe present invention is compared with a polymer electrolyte batteryhaving a flat plate type battery element curved, the former battery hasan extremely low possibility of short-circuit at the end of an electrodeand excellent battery characteristics. Further, in the polymerelectrolyte battery according to the present invention, at least a partof a substantially circular arc part of the semicircular form may have aflat part.

A method for manufacturing a polymer electrolyte battery according tothe present invention comprises a battery element forming step offorming a battery element having a cathode and an anode coiled through apolymer electrolyte; and a thermocompression bonding and forming step ofapplying a thermocompression bonding process to the battery elementbetween a recessed heater block having a curved recessed surface and aprotruding heater block having a curved protruding surface so that asection of the battery element perpendicular to the coiling axis has acurved form.

In the method for manufacturing a polymer electrolyte battery accordingto the present invention constructed as mentioned above, the batteryelement having the cathode and the anode coiled through the polymerelectrolyte undergoes a thermocompression bonding process between therecessed heater block and the protruding heater block so as to becurved. Therefore, according to the method for manufacturing the polymerelectrolyte battery of the present invention, can be manufactured thepolymer electrolyte battery in which, while a manufacturing process issimple, an electrode interface adhesion property is improved, the curvedform can be maintained for a long time, a possibility of short-circuitat the end of the electrode can be reduced and battery characteristicsare desirably maintained.

Further, in a method for manufacturing a polymer electrolyte batteryaccording to the present invention, the battery element may undergo athermocompression bonding process between the recessed heater blockhaving a flat surface part at least in a part of the curved part and theprotruding heater block having a flat surface part at least in a part ofthe curved part so that a section of the battery element perpendicularto the coiling axis has a curved form having a flat part at least in apart thereof.

Further, a method for manufacturing a polymer electrolyte batteryaccording to the present invention comprises: a battery element formingstep of forming a battery element having a cathode and an anode coiledthrough a polymer electrolyte; and a thermocompression bonding andforming step of applying a thermocompression bonding process to thebattery element between a recessed heater block having a curved recessedsurface and a flat surface type heater block having a flat surface sothat a section of the battery element perpendicular to the coiling axishas a substantially semicircular form.

In the method for manufacturing a polymer electrolyte battery accordingto the present invention constructed as mentioned above, the batteryelement having the cathode and the anode coiled through the polymerelectrolyte undergoes a thermocompression bonding process between therecessed heater block and the flat surface type heater block so as tohave a substantially semicircular form. Therefore, according to themethod for manufacturing the polymer electrolyte battery of the presentinvention, can be manufactured the polymer electrolyte battery in which,while a manufacturing process is simple, an electrode interface adhesionproperty is improved, the substantially semicircular form can bemaintained for a long time, a possibility of short-circuit at the end ofthe electrode can be reduced and battery characteristics are desirablymaintained.

Still further, in a method for manufacturing a polymer electrolytebattery according to the present invention, the battery element mayundergo a thermocompression bonding process between the recessed heaterblock having a flat surface part at least in a part of the curved partand the flat surface type heater block having the flat surface so thatthe section of the battery element perpendicular to the coiling axis hasa substantially semicircular form and a flat part is formed at least ina part of a substantially circular arc part.

Still other objects, characteristics or advantages of the presentinvention will become more apparent from the detailed description inaccordance with embodiments of the present invention which will bedescribed below and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing an electronic device towhich a flat plate type polymer electrolyte battery is attached.

FIG. 2 is a perspective view of a polymer electrolyte battery includinga battery element in which a section perpendicular to a coiling axis hasa curved form.

FIG. 3 is a schematic view showing a flat type battery element.

FIG. 4 is a sectional view of main parts showing the flat type batteryelement.

FIG. 5 is a schematic sectional view showing an electronic device towhich a polymer electrolyte battery including a battery element whosesection perpendicular to a coiling axis has a curved form is attached.

FIG. 6 is a perspective view showing a battery element in which asection perpendicular to a coiling axis has a curved form having a flatpart at least in a part thereof.

FIG. 7 is a schematic view showing a state that a flat type batteryelement is inserted into a part between a recessed heater block and aprotruding heater block.

FIG. 8 is a schematic view showing a state that the recessed heaterblock and the protruding beater block are clamped.

FIG. 9 is a schematic view showing a state that the recessed heaterblock and the protruding heater block are opened.

FIG. 10 is a schematic view showing a state that a flat type batteryelement is inserted into a part between a recessed heater block having aflat surface part in the central part of a curved surface part and aprotruding heater block having a flat surface part in the central partof a curved surface part.

FIG. 11 is a perspective view of a polymer electrolyte battery having abattery element in which a section perpendicular to a coiling axis has asubstantially semicircular form.

FIG. 12 is a schematic sectional view showing an electronic device towhich a polymer electrolyte battery having a battery element whosesection perpendicular to a coiling axis has a substantially semicircularform is attached.

FIG. 13 is a perspective view of a battery element in which a sectionperpendicular to a coiling axis has a flat part at least in a part of asubstantially circular arc part.

FIG. 14 is a schematic view showing a state that a flat type batteryelement is inserted into a part between a recessed heater block and aflat surface type heater block.

FIG. 15 is a schematic view showing a state that the recessed heaterblock and the flat surface type heater block are clamped.

FIG. 16 is a schematic view showing a state that the recessed heaterblock and the flat surface type heater block are opened.

FIG. 17 is a schematic view showing a state that a flat type batteryelement is inserted into a part between a recessed heater block having aflat surface part in the central part of a curved surface part and aflat surface type heater block.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Now, embodiments of a polymer electrolyte battery according to thepresent invention will be described in detail by referring to thedrawings.

In a polymer electrolyte battery 1 to which the present invention isapplied, a battery element 2 a in which a section perpendicular to acoiling axis has a curved form is covered with a laminate film 3 made ofan insulating material or the like and sealed under reduced pressure asshown in FIG. 2.

The battery element 2 a is formed by forming a flat type battery element2 b shown in FIG. 3 and including a cathode and an anode coiledlongitudinally through a polymer electrolyte layer in accordance with aforming method as described below so that a section perpendicular to acoiling axis has a curved form.

Specifically shown in FIG. 4, the battery element 2 b includes a cathode6 having cathode active material layers 5 respectively formed on boththe main surfaces of a cathode current collector 4, an anode 9 havinganode active material layers 8 respectively formed on both the mainsurfaces of an anode current collector 7 and polymer electrolyte layers10 formed on the cathode active material layers 5 and polymerelectrolyte layers 11 formed on the anode active material layers 8.Then, the cathode 6 having the polymer electrolyte layers 10 and theanode 9 including the polymer electrolyte layers 11 are laminatedthrough a separator 12, and then, the laminated body is coiled in thelongitudinal direction to form the battery element 2 b. Further, asshown in FIG. 3, a cathode terminal 13 using aluminum is formed at oneend of the cathode current collector 4 and an anode terminal 14 usingcopper or nickel is formed at one end of the anode current collector 7,respectively.

The battery element 2 b is formed as the battery element 2 a with itssection perpendicular to the coiling axis having a curved form as shownin FIG. 2 and then accommodated in the above-described laminate film 3while the cathode terminal 13 and the anode terminal 14 are guidedoutside.

As the cathode current collector 4, may be used aluminum, titanium oralloys of them, etc. The cathode current collector 4 may be formed in afoil shape, a lath form, a punching metal, a net or the like. Thethickness of the cathode current collector 4 is preferably 20 m orlower.

The cathode active material layers 5 are formed by applying on both themain surfaces of the cathode current collector 4 cathode compositemixture slurry obtained by dispersing a cathode composite mixtureincluding a cathode active material, a conductive material and a bindingagent in a solvent.

As the cathode active material, any of conventionally known cathodeactive materials may be employed in such polymer electrolyte batteries.For instance, composite oxides with lithium and transition metals may beused. More specifically, there may be employed materials including onlyone kind of transition metal such as LiCoO₂, LiNiO₂, LiMn₂O₄, LiAlO₂,etc. or materials including two or more kinds of transition metals suchas LiNi_(0.5)Co_(0.5)O₂, LiNi_(0.8)Co_(0.2)O₂, etc.

As the conductive agent, for instance, carbon materials may be used.Further, as the binding agent, for instance, polyvinylidene fluoride canbe used. As the solvent, for instance, N-methylpyrrolidone my be used.

As the anode current collector 7, for instance, copper may be used. Theanode current collector 7 may be configured to be a foil form, a lathform, a punching metal, a net, etc.

The anode active material layers 8 are formed by applying on both themain surfaces of the anode current collector 7 anode composite mixtureslurry obtained by dispersing an anode composite mixture including ananode active material and a binding agent in a solvent.

As the anode active material, any of conventionally known anode activematerials may be employed in such polymer electrolyte batteries. Forinstance, lithium metals, lithium alloys or materials capable ofinserting/extracting lithium may be used.

As the materials capable of inserting/extracting lithium, for instance,carbon materials such as graphite, non-graphitizable carbons,graphitizable carbons, etc. may be employed. More specifically, theremay be utilized, pyrocarbons or coke (pitch coke, needle coke, petroleumcoke), graphite, vitreous carbons, organic polymer compound sinteredbodies (obtained by sintering phenol resins or furan resins at suitabletemperature and carbonizing the sintered products), carbon fibers andactivated carbons, etc. Further, as the materials capable ofinserting/extracting lithium, there may be used polymers such aspolyacetylene or polypyrrole, oxides such as SnO₂, etc.

To the anode composite mixture, a conductive material may be added asrequired. As the conductive material, for instance, carbon materials orthe like may be used. Further, as the binding agent, for instance,polyvinylidene fluoride may be used. As the solvent, for instance,N-methylpyrrolidone may be employed.

As the polymer electrolyte forming the polymer electrolyte layers 10 and11, any kind of polymer electrolytes used in such nonaqueous electrolytebatteries may be used. Especially, a solid polymer electrolyte having aheat sealing property or a thermosetting property and high in itselectrochemical stability or a gel electrolyte obtained by adding aplasticizer to the solid polymer electrolyte can be preferably employed.

The above-described gel electrolyte includes a nonaqueous solvent,electrolyte salt and a matrix polymer.

As the nonaqueous solvent, there may be employed carbonates such asethylene carbonate, propylene carbonate, γ-butyrolactone, dimethylcarbonate, diethyl carbonate, ethyl methyl carbonate, dipropylcarbonate, ethyl propyl carbonate, vinylene carbonate or solventsobtained by replacing hydrogens of these carbonates by halogens, etc.These nonaqueous solvents may be independently used or two or more kindsof them may be mixed together and the mixture may be used.

As the electrolyte salt, there may be used, for instance, LiPF₆, LiClO₄,LiCF₃SO₃, LiAsF₆, LiBF₄, LiN(CF₃SO₃)₂, C₄F₉SO₃Li, etc. One kind of theseelectrolyte salts may be independently used or two or more kinds of themmay be mixed and the mixture may be used.

As the matrix polymer, polymers which can suitably hold nonaqueouselectrolyte solution obtained by dissolving the electrolyte salt in thenonaqueous solvent to be gel are employed. As the specific matrixpolymers, may be used polymers including polyvinylidene fluoride,polyethylene oxide, polypropylene oxide, polyacrylonitrile,polymethacrylonitrile as a repeated unit, however, the matrix polymer isnot limited thereto. As such a thermoplastic matrix polymer, one kind ofpolymer may be independently used or two or more kinds of polymers maybe mixed together and the mixture may be used.

Further, as the matrix polymer, may be utilized polymers in whichmonomers having one or more reactive unsaturated groups in molecules arebridged in nonaqueous electrolyte solution. As the monomer having thereactive unsaturated groups, can be used, for instance, acrylic acid,methyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate,polyethylene glycol monoacrylate, ethoxyethyl methacrylate, methoxyethylmethacrylate, glycidyl acrylate, acryl acrylate, acrylonitrile,diethylene glycol diacrylate, triethylene glycol diacrylate,polyethylene glycol triacrylate, diethylene glycol dimethacrylate, etc.Monomers desired in view of reactivity or polarity may be independentlyused or combined together and the combination thereof may be used.However, the monomers are not limited thereto. As methods forpolymerizing these monomers, for instance, means by heat, ultravioletrays, electron beam or the like may be utilized. A polymerization methodby the heat among these methods in which an electrode layer/a gelelectrolyte layer can be easily formed integrally is most effective.

As the separator 12, porous polyolefine or non-woven fabric or the likecan be employed. Specially, when the diaphragm property of the polymerelectrolytes 10 and 11 is low, the separator 12 is preferably insertedin a suitable manner.

The polymer electrolyte battery 1 constructed as described above has thebattery element 2 a including the cathode 6 and the anode 9 coiledthrough the polymer electrolyte layers 10 and 11 in which a sectionperpendicular to a coiling axis has a curved form. Thus, when thepolymer electrolyte battery 1 is compared with a conventional polymerelectrolyte battery having a flat plate type battery element bent, theelectrolyte battery 1 is extremely low in its possibility ofshort-circuit at the end part of an electrode and has good batterycharacteristics.

Therefore, according to the polymer electrolyte battery 1 to which thepresent invention is applied, since the form of the polymer electrolytebattery 1 can be very easily adapted to the form of the inner space ofan electronic device 20 having a curved surface, the space accommodationefficiency of the polymer electrolyte battery 1 can be improved, asshown in FIG. 5. As a result, a useless space which has been hithertogenerated between the casing of the electronic device and the flat platetype polymer electrolyte battery can be filled with the generatingelement, so that the polymer electrolyte battery can contribute to thevariety of the external form or the compact size of the electronicdevice 20.

In the above-mentioned polymer electrolyte battery 1, although anexample in which the section of the battery element 2 b perpendicular tothe coiling axis has a curved form is described, the present inventionis not limited thereto. For instance, as shown in FIG. 6, the section ofa battery element 2 c perpendicular to a coiling axis may have a curvedform having a flat part 50 at least in a part thereof.

Now, a method for manufacturing the above-described polymer electrolytebattery 1 will be described. When the polymer electrolyte battery 1 ismanufactured, a battery element forming step for forming the flat typebattery element 2 b is initially carried out. Then, a thermocompressionbonding and forming step for applying a thermocompression bondingprocess to the battery element 2 b to form the battery element 2 a whosesection perpendicular to the coiling axis has a curved form.Subsequently, a sealing step for covering the battery element 2 a withthe laminate film 3 and sealing under reduced pressure is carried out.

In the battery element forming step, the cathode 6 and the anode 9 arecoiled through the polymer electrolyte layers 10 and 11 to form the flattype battery element 2 b.

In order to manufacture the cathode 6, the cathode composite mixtureformed by uniformly mixing the cathode active material, the conductivematerial and the binding agent together is dispersed in the solvent toprepare cathode composite mixture slurry. Then, this cathode compositemixture slurry is uniformly applied to both the surfaces of the cathodecurrent collector 4 by, for example, a doctor blade method. Then, a filmin a wet state is dried at high temperature to blow off the solvent andform the cathode active material layers 5.

Then, the cathode terminal 13 is connected to one end of the cathodecurrent collector 4 by a spot welding method or an ultrasonic weldingmethod. The cathode terminal 13 preferably protrudes in the samedirection as that of the anode terminal 14. However, in case ashort-circuit is not generated and a battery performance has no problem,the cathode terminal 13 may protrude in any direction. Further, when aposition to which the cathode terminal 13 is connected has an electricconnection, a place to which the cathode terminal 13 is attached and amethod for attaching the cathode terminal 13 are not limited to aprescribed place or a prescribed method.

In order to manufacture the anode 9, firstly, the anode compositemixture obtained by uniformly mixing the anode active material with thebinding agent is dispersed in the solvent to prepare the anode compositemixture slurry. The conductive material may be added to the anodecomposite mixture as required. Then, the anode composite mixture slurryis uniformly applied to both the surfaces of the anode current collector7 by, for instance, a doctor blade method or the like. Subsequently, afilm in a wet state is dried at high temperature to blow off the solventand form the anode active material layers 8.

After that, the anode terminal 14 is connected to one end of the anodecurrent collector 7 by a spot welding method or a ultrasonic weldingmethod. The anode terminal 14 is preferably extended in the samedirection as that of the cathode terminal 13. However, in case ashort-circuit is not generated and a battery performance has nottrouble, the anode terminal 14 may be extended in any direction.Further, when a position to which the anode terminal 14 is connected hasan electric connection, any place to which the anode terminal 14 isattached and any method for attaching the anode terminal 14 may beemployed without limitation.

Then, polymer electrolyte solution including, for instance, solvent suchas dimethyl carbonate, a plasticizer and matrix polymer is applied tothe cathode active material layers 5 and the anode active material layer8, and then, dimethyl carbonate is vaporized and removed so that the gelpolymer electrolyte layers 10 and 11 are formed.

Subsequently, the band shape cathode 6 on which the polymer electrolytelayers 10 are formed and the band shape anode 9 on which the polymerelectrolyte layers 11 are formed are longitudinally coiled through theseparator 12 to obtain the flat type battery element 2 b.

In the thermocompression bonding and forming step, the thermocompressionbonding process is applied to the battery element 2 b between a recessedheater block having a curved recessed surface and a protruding haterblock having a curved protruding surface so that the section of thebattery element 2 b perpendicular to the coiling axis has a curved form.

When the thermocompression bonding process is applied to the batteryelement 2 b, the flat type battery element 2 b is firstly insertedbetween the recessed heater block 21 and the protruding heater block 22as shown in FIG. 7. Then, as shown in FIG. 8, the recessed heater block21 and the protruding heater block 22 are clamped to perform athermocompression bonding process by properly adjusting the temperatureand pressure of the heater blocks 21 and 22.

Then, as shown in FIG. 9, the recessed heater block 21 and theprotruding heater block 22 are opened so that the battery element 2 awhose section perpendicular to the coiling axis has a curved form isreleased therefrom.

The flat type battery element 2 b is subjected to a thermocompressionbonding process to be formed by using the recessed heater block 21 andthe protruding heater block 22 as described above, so that the batteryelement 2 a in which the section perpendicular to the coiling axis hasthe curved form is obtained.

In the thermocompression bonding and forming step, since the entire bodyof the battery element 2 b undergoes the thermocompression bondingprocess by using the recessed heater block 21 and the protruding heaterblock 22 so that the section of the battery element perpendicular to thecoiling axis has the curved form, the battery element 2 a having anexcellent electrode interface adhesion property, provided with a goodelectrode/electrolyte interface for the polymer electrolyte battery 1and capable of holding the curved form for a long time can be obtained.

In the sealing step, the battery element 2 a in which the section of thebattery element perpendicular to the coiling axis has the curved form isheld by the laminate films 3 and the outer peripheral edge parts of thelaminate films 3 are heat-sealed under reduced pressure.

Thus, the polymer electrolyte battery 1 in which the battery element 2 ais sealed in the laminate films 3 is obtained.

According to the method for manufacturing the polymer electrolytebattery 1 having the above-described steps, the flat type batteryelement 2 b formed by coiling the cathode 6 and the anode 9 through thepolymer electrolyte layers 10 and 11 is subjected to thethermocompression bonding process by using the recessed heater block 21and the protruding heater block 22 so that the section of the batteryelement 2 b perpendicular to the coiling axis thereof has the curvedform.

Therefore, according to the method for manufacturing the polymerelectrolyte battery 1, can be manufactured the polymer electrolytebattery 1 in which an electrode interface adhesion property is moreimproved, the curved form in section perpendicular to the coiling axiscan be held for a longer time, a possibility of short-circuit in the endpart of the electrode is more reduced and the battery characteristicsare more desirably maintained, while manufacturing processes are simple,than a conventional polymer electrolyte battery having a flat plate typebattery element curved produced by a conventional battery producingmethod.

In the above-described method for manufacturing the polymer electrolytebattery 1, although a case in which the battery element 2 a formed insuch a way that the section of the battery element perpendicular to thecoiling axis has the curved form is covered with the laminate film 3 ismentioned, the present invention is not limited thereto. After the flattype battery element 2 b is covered and sealed with the laminate film 3,the obtained battery element may be inserted into a part between therecessed heater block 21 and the protruding heater block 22, and then,the battery element may be subjected to the thermocompression bondingprocess in a similar method to that described above.

Further, in the above-described method for manufacturing the polymerelectrolyte battery 1, although a case in which the battery element 2 bis subjected to the thermocompression bonding process between therecessed heater block having the curved recessed surface and theprotruding heater block having the curved protruding surface so that thesection of the battery element 2 b perpendicular to the coiling axisthereof has the curved form is mentioned, the present invention is notlimited thereto. For instance, as shown in FIG. 10, the above-describedbattery element may be subjected to the thermocompression bondingprocess between a recessed heater block 52 having a flat surface part 51at least in a part of a curved part and a protruding heater block 54having a flat surface part 53 at least in a part of a curved part. Abattery element 2 c obtained in such a manner has a curved form so thatthe section of the battery element 2 c perpendicular to a coiling axishas a flat part 50 at least in a part thereof.

A silicon rubber sheet 55 is preferably arranged on at least one of thesurfaces of the recessed heater block 52 and the protruding heater block54 (in this case, the recessed heater block 52) opposed to the batteryelement 2 c. The silicon rubber sheet 55 is arranged so that heat andpressure can be uniformly applied to the battery element 2 c.

Now, another polymer electrolyte battery to which the present inventionis applied will be described below.

In a polymer electrolyte battery 31 according to another embodiment towhich the present invention is applied, a battery element 32 a in whicha section of the battery element perpendicular to a coiling axis has asubstantially semicircular form is covered with a laminate film 3 madeof an insulating material and sealed under reduced pressure.

The polymer electrolyte battery 31 has the same construction as that ofthe above-described polymer electrolyte battery 1 except that thebattery 31 has the battery element 32 a in which the sectionperpendicular to the coiling axis has the substantially semicircularform. Therefore, the same members as those of the above-describedpolymer electrolyte battery 1 are designated by the same referencenumerals and the explanation thereof is omitted.

Since the polymer electrolyte battery 31 includes the battery element 32a having a cathode 6 and an anode 9 coiled through polymer electrolytelayers 10 and 11 so that the section of the battery elementperpendicular to the coiling axis has the substantially semicircularform, the polymer electrolyte battery 31 is extremely low in itspossibility of short-circuit at the end part of an electrode and good inits battery characteristics, as compared with an existing polymerelectrolyte battery having a flat plate type battery element bent.

Therefore, according to the polymer electrolyte batter 31 to which thepresent invention is applied, since the form of the polymer electrolytebattery 31 can be outstandingly easily adapted to the form of the innerspace of an electronic device 40 having a curved surface; as shown inFIG. 12, so that the space accommodation efficiency of the polymerelectrolyte battery 31 can be improved. As a result, a useless spacewhich has been hitherto generated between the casing of the electronicdevice and the flat plate type polymer electrolyte battery can be filledwith the generating element, so that the polymer electrolyte battery cancontribute to the diversity of the external form and the compact size ofthe electronic device 40.

In the above-described polymer electrolyte battery 31, although a casein which the section of the battery element 32 a perpendicular to thecoiling axis has the substantially semicircular form is mentioned, thepresent invention is not limited thereto. For instance, as shown in FIG.13, the polymer electrolyte battery may be formed so that the section ofthe battery element 32 c perpendicular to a coiling axis has asubstantially semicircular form including a flat part 60 at least in apart of a substantially circular arc part.

Now, a method for manufacturing the above-described polymer electrolytebattery 31 will be described. When the polymer electrolyte battery 31 ismanufactured, a battery element forming step for forming the flat typebattery element 32 b is initially carried out. Then, a thermocompressionbonding and forming step for applying a thermocompression bondingprocess to the battery element 32 b to form the battery element 32 awhose section perpendicular to the coiling axis has a substantiallysemicircular form. Subsequently, a sealing step for covering the batteryelement 32 a with the laminate film 3 and sealing it under reducedpressure is carried out.

Since the battery element forming step in the method for manufacturingthe polymer electrolyte battery 31 is the same as the battery elementforming step in the method for manufacturing the polymer battery 1, anexplanation thereof is omitted.

In the thermocompression bonding and forming step, the thermocompressionbonding process is applied to the battery element 32 b between arecessed heater block having a curved recessed surface and a flatsurface type hater block having a flat surface so that the section ofthe battery element 32 b perpendicular to the coiling axis has asubstantially semicircular form.

When the thermocompression bonding process is applied to the batteryelement 32 b, the flat type battery element 32 b is firstly insertedbetween the recessed heater block 41 and the flat surface type heaterblock 42 as shown in FIG. 14. Then, as shown in FIG. 15, the recessedheater block 41 and the flat surface type heater block 42 are clamped toperform a thermocompression bonding process by properly adjusting thetemperature and pressure of the heater blocks 41 and 42.

Then, as shown in FIG. 16, the recessed heater block 41 and the flatsurface type heater block 42 are opened so that the battery element 32 awhose section perpendicular to the coiling axis has a substantiallysemicircular form is released therefrom.

The flat type battery element 32 b is subjected to a thermocompressionbonding process to be formed by using the recessed heater block 41 andthe flat surface type heater block 42 as described above, so that thebattery element 32 a in which the section perpendicular to the coilingaxis has the curved form is obtained.

In the thermocompression bonding process and forming step, since theentire body of the battery element 32 b undergoes the thermocompressionbonding process by using the recessed heater block 41 and the flatsurface type heater block 42 so that the section of the battery elementperpendicular to the coiling axis has the substantially semicircularform, the battery element 32 a having an excellent electrode interfaceadhesion property, provided with a good electrode/electrolyte interfacefor the polymer electrolyte battery 31 and capable of holding thesubstantially semicircular form for a long time can be obtained.

In the sealing step, the battery element 2 a in which the section of thebattery element perpendicular to the coiling axis has the substantiallysemicircular form is held by the laminate films 3 and the outerperipheral edge parts of the laminate films 3 are heat-sealed underreduced pressure.

Thus, the polymer electrolyte battery 1 in which the battery element 2 ais sealed in the laminate films 3 is obtained.

According to the method for manufacturing the polymer electrolytebattery 31 having the above-described steps, the flat type batteryelement 32 b formed by coiling the cathode 6 and the anode 9 through thepolymer electrolyte layers 10 and 11 is subjected to thethermocompression bonding process by using the recessed heater block 41and the flat surface type heater block 42 so that the section of thebattery element 32 b perpendicular to the coiling axis thereof has thesubstantially semicircular form.

Therefore, according to the method for manufacturing the polymerelectrolyte battery 31, can be manufactured the polymer electrolytebattery 31 in which an electrode interface adhesion property is moreimproved, the substantially semicircular form in section perpendicularto the coiling axis can be held for a longer time, a possibility ofshort-circuit in the end part of the electrode is more reduced and thebattery characteristics are more desirably maintained, whilemanufacturing processes are simple, than a conventional polymerelectrolyte battery having a plate type battery element curved producedby a conventional battery producing method.

In the above-described method for manufacturing the polymer electrolytebattery 31, although a case in which the battery element 32 a formed insuch away that the section of the battery element perpendicular to thecoiling axis has the substantially semicircular form is covered with thelaminate film 3 is mentioned, the present invention is not limitedthereto. After the flat type battery element 32 b is covered and sealedwith the laminate film 3, the obtained battery element may be insertedinto a part between the recessed heater block 41 and the flat surfacetype heater block 42, and then, the battery element may be subjected tothe thermocompression bonding process in a similar method to thatdescribed above.

Further, in the above-described method for manufacturing the polymerelectrolyte battery 31, although a case in which the battery element 32b is subjected to the thermocompression bonding process between therecessed heater block having the curved recessed surface and the flatsurface type heater block so that the section of the battery element 32a perpendicular to the coiling axis thereof has the semicircular form ismentioned, the present invention is not limited thereto. For instance,as shown in FIG. 17, the above-described battery element may besubjected to the thermocompression bonding process between a recessedheater block 62 having a flat surface part 61 at least in a part of acurved part and a flat surface type heater block 63. A battery element32 c obtained has a form in which the section of the battery element 32c perpendicular to a coiling axis has a substantially semicircular formincluding a flat part 60 at least in a part of a substantially circulararc part, as shown in FIG. 13.

A silicon rubber sheet 55 is preferably arranged on either one of thesurfaces of the recessed heater block 62 and the flat surface typeheater block 63 (in this case, the recessed heater block 62) opposed tothe battery element 32 c. The silicon rubber sheet 55 is arranged sothat heat and pressure can be uniformly applied to the battery element32 c.

EXAMPLES

Now, Examples in which polymer electrolyte batteries to which thepresent invention is applied are actually manufactured and a ComparativeExample in which a polymer electrolyte battery is manufactured tocompare this battery with the batteries of the Examples will bedescribed on the basis of specific experimental results.

Example 1

[Manufacture of Cathode]

As components of a cathode composite mixture, LiCoO₂ of 92 parts byweight as a cathode active material, powdered graphite of 5 parts byweight as a conductive material and powdered polyvinylidene fluoride of3 parts by weight as a binding agent were measured and used. Then, thesecomponents were dispersed in N-methyl pyrrolidone to prepare the slurryof the cathode composite mixture.

The cathode composite mixture thus prepared was uniformly applied toboth the surfaces of a cathode current collector made of an aluminumfoil (having the thickness of 20 m), and then dried under reducedpressure at the temperature of 100° C. for 24 hours so that cathodeactive material layers were formed. Then, the cathode active materiallayers were compression-molded by using a roll press machine to form acathode sheet. After that, the cathode sheet was cut to manufacture aband shape cathode having length of 50 mm and width of 300 mm. As acathode lead, an aluminum ribbon was welded to a part of the cathodecurrent collector to which the cathode active material was not applied.

[Manufacture of Anode]

As components of an anode composite mixture, artificial graphite of 91parts by weight as an anode active material and powdered polyvinylidenefluoride of 9 parts by weight as a binding agent were measured andtaken. Then, these components were dispersed in N-methyl pyrrolidone toprepare the slurry of the anode composite mixture.

The anode composite mixture thus prepared was uniformly applied to boththe surfaces of an anode current collector made of a copper foil (havingthe thickness of 15 m), and then dried under reduced pressure at thetemperature of 120° C. for 24 hours so that anode active material layerswere formed. Then, the anode active material layers werecompression-molded by using a roll press machine to form an anode sheet.After that, the anode sheet was cut to manufacture a band shape anodehaving length of 52 mm and width of 320 mm. As an anode lead, a nickelribbon was welded to a part of the anode current collector to which theanode active material was not applied.

[Manufacture of Polymer Electrolyte]

As the respective components of a plasticizer, ethylene carbonate of42.5 parts by weight and propylene carbonate of 42.5 parts by weight asnonaqueous solvent, LiPF₆ of 15 parts by weight as electrolyte salt weremeasured and used. Then, these components were mixed together to preparethe plasticizer.

Subsequently, as the respective components of polymer solution, theplasticizer of 30 parts by weight, polyvinylidene fluoride-co-hexafluoropropylene of 10 parts by weight and dimethyl carbonate of 60 parts byweight were measured and employed. Then, these components were mixed anddissolved to prepare polymer electrolyte solution.

[Manufacture of Polymer Electrolyte Battery]

After the polymer electrolyte solution prepared as described above wasapplied to the cathode active materials on both the surfaces of thecathode and to the anode active materials on both the surfaces of theanode, these active materials were left under an environment at ambienttemperature for 8 hours, and dimethyl carbonate was vaporized andremoved so that gel electrolyte layers (having the thickness of 100 m)were formed.

Then, the band shape cathode on which the gel electrolyte layers wereformed and the band shape anode on which the gel electrolyte layers wereformed were laminated through a separator made of porous polyolefine,and the laminated body was coiled longitudinally to obtain a flat typebattery element. This flat type battery element was sandwiched inbetween by outer package films and the outer peripheral edges of theouter package films were heat-sealed under reduced pressure. Thus, theflat type battery element was sealed in the outer package films. As theouter package film, was employed a film having an aluminum foilsandwiched in between a pair of polyolefine resin films.

Subsequently, the flat type battery element sealed in the outer packagefilms was formed by a thermocompression bonding process of 10 kgf/cm²for 5 minutes under an environment at the temperature of 85° C. byemploying a heat press machine having a recessed heater block and aprotruding heater block so that a polymer electrolyte battery whosesection perpendicular to a coiling axis had a curved form was obtained.

Example 2

A polymer electrolyte battery was manufactured in the same manner asthat of the Example 1 except that a flat type battery element sealed inouter package films was subjected to a thermocompression bonding processby using a heat press machine including a recessed heater block and aflat surface type heater block so that the section of the batteryelement perpendicular to a coiling axis had a substantially semicircularform.

Example 3

A polymer electrolyte battery was manufactured in the same manner asthat of the Example 1 except that a flat type battery element sealed inouter package films was subjected to a thermocompression bonding processby using a heat press machine including a recessed heater block having aflat surface part in the central part of a curved surface part and asilicon rubber sheet with the thickness of 1 mm stuck thereto and aprotruding heater block having a flat surface part in the central partof a curved surface part so that the section of the battery elementperpendicular to a coiling axis had a curved form having a flat part atleast in a part thereof.

Example 4

A polymer electrolyte battery was manufactured in the same manner asthat of the Example 1 except that a flat type battery element sealed inouter package films was subjected to a thermocompression bonding processby using a heat press machine including a recessed heater block having aflat surface part in the central part of a curved surface part and asilicon rubber sheet with the thickness of 1 mm stuck thereto and anentirely flat plate type heater block so that the section of the batteryelement perpendicular to a coiling axis had a substantially semicircularform having a flat part at least in a part of a substantially circulararc part.

Comparative Example 1

A polymer electrolyte battery was manufactured in the same manner asthat of the Example 1 except that a flat type battery element sealed inouter package films was subjected to a thermocompression bonding processby using a heat press machine including a pair of flat surface typeheater blocks so that the section of the battery element perpendicularto a coiling axis had a substantially rectangular form.

A charging and discharging test was carried out to the respectivepolymer electrolyte batteries of the Example, 1, the Example 2 and theComparative Example 1 manufactured as described above to evaluatebattery characteristics. The theoretical capacity of each of the polymerbatteries of the Example 1, the Example 2 and the Comparative Example 1is 600 mAh.

[Charging and Discharging Test]

Initially, after a constant-current and constant-voltage chargingoperation of 1 C (600 mA) and 4.2 V was carried out, a constant-currentdischarging operation of 1 C with 3V cut off was carried out to measurean initial discharging capacity.

Then, charging and discharging cycles were repeated 500 times to measurea discharging capacity after 500th cycle. Then, the ratio of thedischarging capacity after the 500th cycle relative to the initialdischarging capacity was obtained and it was considered to be adischarging capacity maintaining/retention ratio.

The above-described measured results are shown in Table 1.

TABLE 1 Capacity Initial Discharging Maintaining/retention Capacity(mAh) Ratio (%) Example 1 592 83 Example 2 590 81 Example 3 593 83Example 4 591 82 Comparative 591 82 Example 1

As apparent from the Table 1, the polymer electrolyte batteries of theExamples 1 to 4 has a high discharging capacity and excellent cycliccharacteristics similar to those of the polymer electrolyte battery ofthe Comparative Example 1.

Therefore, it was understood that even when the flat type batteryelement having the cathode and the anode coiled through the polymerelectrolyte was subjected to the thermocompression bonding process bythe above-described heat press machine so that the section of thebattery element perpendicular to the coiling axis had an epoch-makingform such as the curved form or the substantially semicircular form inthe polymer electrolyte battery, the battery characteristics wereeffectively maintained.

INDUSTRIAL APPLICABILITY

Since the polymer electrolyte battery according to the present inventionincludes the battery element having the cathode and the anode coiledthrough the polymer electrolyte in which the section of the batteryelement perpendicular to the coiling axis has the curved form, theabove-described battery of the present invention is extremely low in itspossibility of short-circuit at the end of the electrode and good in itsbattery characteristics, as compared with the polymer electrolytebattery having the flat plate type battery element bent.

1. A polymer electrolyte battery comprising: a wound battery elementincluding a cathode comprising an elongate cathode collector having atleast two faces on which cathode active material layers are formed; ananode comprising an elongate anode collector having at least two faceson which anode active material layers are formed; and a polymerelectrolyte formed between said cathode and said anode; wherein thewound battery element has a first longitudinal surface, a secondlongitudinal surface opposite said first longitudinal surface, a firstrounded lateral side, a second rounded lateral side opposite said firstrounded lateral side, and a winding axis; and wherein a section of saidfirst longitudinal surface of the wound battery element takenperpendicular to the winding axis has a curved portion between saidfirst rounded lateral side and said second rounded lateral side, asection of said second longitudinal surface of the wound battery elementtaken perpendicular to the winding axis has a curved portion betweensaid first rounded lateral side and said second rounded lateral side,and the curved portion of the first longitudinal surface is parallel tothe curved portion of the second longitudinal surface.
 2. The polymerelectrolyte battery according to claim 1 wherein the polymer electrolytecomprises a gel electrolyte.
 3. The polymer electrolyte batteryaccording to claim 1 wherein the curved portion of the firstlongitudinal surface and the second longitudinal surface of the woundbattery element is formed by thermocompression bonding.
 4. A polymerelectrolyte battery comprising: a wound battery element including acathode comprising an elongate cathode collector having at least twofaces on which cathode active material layers are formed; an anodecomprising an elongate anode collector having at least two faces onwhich anode active material layers are formed; and a polymer electrolyteformed between said cathode and said anode; wherein the wound batteryelement has a first longitudinal surface, a second longitudinal surfaceopposite said first longitudinal surface, a first rounded lateral side,a second rounded lateral side opposite said first rounded lateral side,and a winding axis; and wherein the first longitudinal surface isgenerally perpendicular to the winding axis and has a substantiallysemicircular portion extending outwardly from the winding axis; andwherein the second longitudinal surface is generally parallel to thewinding axis and includes a substantially straight portion.
 5. Thepolymer electrolyte battery according to claim 4 wherein the polymerelectrolyte comprises a gel electrolyte.
 6. The polymer electrolytebattery according to claim 4 wherein the substantially semicircularportion of the first longitudinal surface of the wound battery elementis formed by thermocompression bonding.
 7. A polymer electrolyte batterycomprising: a wound battery element including a cathode comprising anelongate cathode collector having at least two faces on which cathodeactive material layers are formed; an anode comprising an elongate anodecollector having at least two faces on which anode active materiallayers are formed; and a polymer electrolyte formed between said cathodeand said anode; wherein the wound battery element has a firstlongitudinal surface, a second longitudinal surface opposite said firstlongitudinal surface, a first rounded lateral side, a second roundedlateral side opposite said first rounded lateral side, and a windingaxis; and wherein the first longitudinal surface is generallyperpendicular to the winding axis and includes a curved portion betweensaid first rounded lateral side and said second rounded lateral sideextending circumferentially from the winding axis; and wherein thesecond longitudinal surface is generally parallel to the winding axisand includes a substantially straight portion.
 8. The polymerelectrolyte battery according to claim 7 wherein the polymer electrolytecomprises a gel electrolyte.
 9. The polymer electrolyte batteryaccording to claim 7 wherein the curved portion of the firstlongitudinal surface of the wound battery element is formed bythermocompression bonding.